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Oh, it's too terrible! >:-{
He tells that he has used his unit for two months only and it was not like that when it was new! Indeed, in the same thread, there are users of K-7, K20D and K10D report the same, here, here and here, respectively.
So, this issue seems to be not uncommon. And the really worrisome thing is that it is found to be persistent since the first "Weather-Resistant" Pentax DSLR model K10D, back to 2007. The most strangest thing is that it happens mostly for those Pentax WR bodies, but rarely heard for non-WR entry-level Pentax DSLR bodies, on the other hand. Well, it seems that the weather-sealing is actually the culprit to this issue! E.g., when it was just not properly assembled out of the Pentax factory or when the sealing rubber and/or other materials are changing its/their state(s) over time?? :-o
Update (10-11):-
Thanks to Blog reader "calluses", we have the following yet another report from a Japanese user for exactly the same issue, also for a Silver K-5:-
(Source: http://d.hatena.ne.jp/hisway306/20110324/1300971454#seemore, in Japanese, Google English translation can be found here)
It is told that the above dust accumulated inside the LCD just from the very beginning and thus the user immediately asked for a direct replacement from the dealer and he got his replacement unit without any difficulty. It is also told that the replacement unit of his have not had the same issue after then.
Update (10-13):-
Yet here is another report of the same issue, for an ordinary black K-5:-
http://forum.xitek.com/showthread.php?threadid=924323
(in Chinese, English Here (Google-translated))
Of course, the user is pissed off. >:-(